Polymerase Chain Reaction

The polymerase Chain Reaction (PCR) is a widely used technique to amplify a specific DNA segment without using bacteria. Basically you take a sample of DNA that you want to amplify, mix it with all four deoxyribose nucleotides, add a temperature resistant DNA polymerase, and two short synthetic DNA fragments, called oligonucleotides, that act as primers and place them into the PCR machine. When the machines heats up to 92+ ^oC, the DNA strand separates. As the temperature cools, the complementary nucleotides bind to the exposed nucleotides of one of the DNA strands, the DNA polymerase does its job and you have twice as much DNA as you started with. By continuing the heat-cool cycle, it is possible to double the amount of DNA with each cycle. The PCR has been used to solve murders from a very minute amount of blood or semen and also by obtaining DNA from body hair.

• Where would you find a DNA polymerase that can survive temperatures above 92 ^oC?
• Why is it necessary to add primers to the mixture?
• If each cycle of the PCR takes 30 minutes, how long will it take to amplify a DNA sample 40 fold?